In Part II, the enthalpy change of dissolution of ammonium sulfate will be deriv

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In Part II, the enthalpy change of dissolution of ammonium sulfate will be derived from the temperature change associated with dissolving the solid in water. (NH_4)_2SO_4(s) rightarrow (NH_4)_2SO_4(aq) Delta H_dissolution Additional information can be found in thermochemical handbooks for the enthalpies of formation of aqueous ammonia, Delta H_f(NH_3(aq)), and of sulfuric acid, Delta H_f(H_2SO_4(aq)). 1/2 N_2(g) + 3/2 H_2(g) rightarrow NH_3(aq) Delta H_f(NH_3(aq)) = - 80.3 kJ/mol and H_2(g) + S(s) + 2O_2(g) rightarrow H_2SO_4(aq) Delta H_f(H_2SO_4(aq)) = - 909 kJ/mol The enthalpy of formation per mole of any compound, Delta H_f, is the enthalpy change accompanying formation of one mole of that compound from the pure elements in their standard states. Write the chemical equation for which Delta H_f [(NH_4)_2SO_4(s)] applies:

Explanation / Answer

2NH3(aq) + H2SO4(aq) ------> [NH4]2SO4 (s)

1/N2 + 3/2 H2 -----NH3 (aq)

delta Hf = -80.3 KJ/mol

For 2 moles ===> delta Hf = -160.6 KJ

H2 + S + 2O2 -----> H2SO4

delta Hf = -909 KJ/mol

delta Hf of [NH4]2 SO4 = 2*delta Hf of NH3 + delta Hf of H2SO4 = -1069.6 KJ

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